Typical modern appliances often employ electrical control circuits to regulate operation thereof. These electrical control circuits typically include both digital controls that control the operational programming of the appliances, as well as electro-mechanical components for actually controlling the opening and closing of valves, door locks, etc. in the appliance. The control of these electro-mechanical devices, for example solenoid control valves, is accomplished by energizing an electrical coil to create a magnetic field that moves a plunger or other type of valve stem to open or close the valve. When the electrical coil is de-energized, a spring is often used to return the plunger or valve stem to its starting or quiescent position.
Because there has been a significant volume increase in the demand for such electro-mechanical components, the demands on manufacturers of such components from both a price and reliability standpoint have increased significantly as well.
The typical electrical coil used on water valves in the appliance industry includes a molded plastic spool. This molded spool typically includes molded-in or otherwise attached electrical contacts that will serve as the electrical interface to the control circuitry. To keep the size of the electrical coil small, a very fine gauge magnetic wire is then wound on the spool. The number of windings on the coil can vary, but typically includes several thousand windings to generate sufficient magnetic force within the center of the spool to properly actuate the plunger or valve stem. To achieve this large number of windings efficiently, an automatic winding machine is used to wind the wire onto the molded spool.
Each end of the coil of wire wound on the spool is attached to one of the two electrical terminals during the manufacturing process. Typically, each end of this fine gauge wire is soldered onto one of the two electrical terminals. Unfortunately, since the soldering process requires physical touching of the wire, there is risk during this process that the wire may be weakened or broken. This is particularly problematic in coils that are encapsulated after the winding and terminal attachment processes are complete because the process of encapsulation itself typically causes stress on the wire at the connection point. Therefore, the damage may not be readily apparent until the entire manufacturing process of the coil is completed. A rejection of this point is quite costly to the manufacturer as the entire encapsulated coil must be scrapped.
There exists, therefore, a need in the art for improved method of manufacturing electrical coils that reduces the reject rate resulting from soldered connection failures between the electrical terminals and the fine gauge magnetic wire.